Abstract
In reservoirs with bottom-water drives, water coning has historically been a producing problem. Prior to the use of high-speed problem. Prior to the use of high-speed computers, the coning problem practically defied solution. This paper discusses a study of water coning in the Oil Creek reservoir of the North Antioch field, which was made utilizing an r-z, two-phase compressible coning model. The model matches water-cut history and predicts future performance. The study points up the importance performance. The study points up the importance of variation in vertical permeability on the coning phenomenon. More particularly, it shows the effects of a continuous 4-ft zone of low permeability which occurs in the reservoir. permeability which occurs in the reservoir. Coning characteristics of wells in which the original oil-water contact was located above the zone are compared with those in which the original contact was below the zone. The study indicated that the reservoir could safely be produced at rates that would greatly increase produced at rates that would greatly increase the present worth value of the reserves without materially affecting the ultimate recovery.
Introduction
The North Antioch field is located in the northwest part of Garvin County, Okla. The field was discovered in May, 1965, with the drilling of Coastal States' J. R. Winchester No. 1. As the field developed, it became obvious that the oil reserves in the Oil Creek reservoir were of substantial proportions. Development was essentially complete by Oct., 1966. Because of a rather unusual combination of reservoir and fluid characteristics and the obvious possibilities for increasing recoverable reserves, possibilities for increasing recoverable reserves, reducing costs and increasing present worth value through proper operation, the decision was made to utilize some advanced forms of reservoir modeling to predict the results of various possible methods of operation of the field. This paper presents the results obtained from modeling and recommendations for future operations in the field.
RESERVOIR CHARACTERISTICS
The Oil Creek reservoir of the North Antioch field is made up of approximately 108 ft of fairly uniform and clean Ordovician sandstone found at a depth of approximately 6,500 ft subsea or 7,500 ft subsurface. Through coring and analysis of logs, it was determined that the average porosity and permeability of the sand are 17.32 percent and 350 md, respectively. Fig. 1 is a portion of a typical electric log of the Oil Creek sand in the field. Table 1 shows the results of core analysis on two cores taken from the Oil Creek reservoir. The most striking of the characteristics of the sand is its uniformity as indicated by the SP portion of the log and the core analysis. There is one noticeable exception to the uniformity and that is the portion marked "barrier" on Fig. 1. portion marked "barrier" on Fig. 1.
